基于石英增强光声光谱的气体传感技术研究进展

Research progress of quartz-enhanced photoacoustic spectroscopy based gas sensing

基于石英增强光声光谱(quartz-enhanced photoacoustic spectroscopy, QEPAS)的气体传感技术具有系统体积小、成本低、环境适应性强等优点,是目前一种重要的光谱式痕量气体检测方法.探测灵敏度是传感器系统的重要指标,关系到能否满足实际应用,因此,本文从提高QEPAS传感系统灵敏度的角度出发,总结了常见的技术手段,包括采用高功率激发光源增大激发强度、采用与分子基频/强吸收带相匹配的激光源来增大吸收强度、采用声波共振腔增大音叉处的声波强度、采用低共振频率石英音叉提高能量积累时间、采用多光程来增大光与气体的相互作用长度等方法,并对其优缺点分别进行了阐述.针对工程应用问题,本文主要讨论了全光纤化和传感系统小型化,并以载人航天领域的应用为例进行了例证.最后,对进一步提高QEPAS传感技术灵敏度的方法进行了展望.

Laser spectroscopy based techniques have the advantages of high sensitivities,high selectivities,noninvasiveness and in situ,real-time observations.They are widely used in numerous fields,such as environmental monitoring,life science,medical diagnostics,manned space flight,and planetary exploration.Owing to the merits of low cost,compact volume and strong environment adaptability,quartz-enhanced photoacoustic spectroscopy(QEPAS)based sensing is an important laser spectroscopy-based method of detecting the trace gas,which was invented in 2002.Detection sensitivity is a key parameter for gas sensors because it determines their real applications.In this paper,focusing on the detection sensitivity,the common methods for QEPAS are summarized.High power laser including amplified diode laser by erbium doped fiber amplifier(EDFA),and quantum cascade laser are used to improve the excitation intensity of acoustic wave.The absorption line of gas molecules located at the fundamental bands of mid-infrared region is adopted to increase the laser absorption strength.Micro-resonator is employed to enhance the generated acoustic pressure by forming a standing wave cavity.Quartz tuning forks(QTFs)with low resonant frequency are used to increase the accumulation time of acoustic energy in itself.Multi-pass strategy is utilized to amplify the action length between laser beam and target gas in the prongs of QTF.The advantages and disadvantages of the above methods are discussed respectively.For the issues in real applications,the all-fiber strucure in near-infared region and mid-infrared region and miniaturization using three-dimensional(3D)printing technique for QEPAS sensor are summarized.A QEPAS technique based multi-gas sensor is used to quantify the concentration of carbon monoxide(CO),carbon dioxide(CO_(2)),hydrogen cyanide(HCN),and hydrogen chloride(HCl)for post-fire cleanup aboard spacecraft,which is taken for example for the real application.Finally,the methods of further improving the sensitivity of QEPAS sensor are proposed.